Mar. 22, 1924 
Nematode Disease Caused by Tylenchus tritici 
949 
Although a relatively high temperature seems to be conducive to the 
opening of the galls, it is not favorable for infection. High temperature 
causes such rapid growth of the plants that before the larvae can effect a 
general invasion the most susceptible period of the plant has passed. 
Wheat plants grown in a warm greenhouse from infested seed show little 
infection, while in the cooler soil of the field, a general invasion of the 
plants usually occurs. Experiments in soil-temperature tanks indicate 
that infection occurs more readily at 12 0 and 16 0 C. than at 20°, 24 0 , and 
28°. Prelude wheat was sown in the field at Madison, Wis., in July, 
1921, and the soil was heavily inoculated with galls. The mean soil 
temperature for the four weeks after sowing was 8o° P. (26.6° C.). The 
plants grew to maturity and produced healthy heads. However, when 
sown in cold soil in early spring and inoculated with galls, Prelude wheat 
produced practically no uninfected heads. This affords additional evi¬ 
dence that temperature is an important factor in infection. 
The nematode larvae seem unable to invade the plant before the 
coleoptile has begun to unclasp or loosen about the young stem. Hun¬ 
dreds of wheat seedlings from heavily infested soil were examined and 
in no case were larvae ever found while the coleoptile was still firm about 
the base of the plant. But plants with this primary sheath slightly 
loosened, frequently contained larvae in abundance. Often they were 
found just within the loosening coleoptile and occasionally at the edge 
as though they were in the act of entering. At a slightly later stage, they 
were invariably found between the leaf sheaths near the growing point. 
How long after the loosening of the coleoptile it remains possible for 
nematode larvae to invade the plant and bring about infection remains 
to be determined. Sommerville (23) sowed wheat in pots November 8 
and kept them in a “cold greenhouse'’ (he does not state at what tem¬ 
perature) until December 16 when he placed them in the open. On 
April 4 he added 20 “cockles" (galls) to each pot. The wheat was har¬ 
vested August 5 and “where the addition of ‘cockles’ was delayed for 
five months after planting, infection was practically as complete as 
when ‘cockles’ were sown with the seed.’’ Marcinowski (17) claims to 
have secured infection by spraying a water suspension of larvae on plants 
of considerable size. 
The writer placed a suspension of active larvae at the base of plants 
6 to 8 inches tall, 16 days after sowing in a warm greenhouse, and 9 days 
later pronounced symptoms were observed. Likewise unopened galls 
placed near the plants 12 days after sowing produced characteristic 
symptoms of nematode injury 30 days later. From these and other 
observations, it may be tentatively assumed that the period during which 
the nematodes can invade the plant and bring about infection extends 
from the loosening of the coleoptile to the elongation of the culm, that 
is, as long as the terminal growing bud or embryonic spike is located 
near the base of the plant. Larval suspensions injected into the flowers 
at various stages of growth from the time the plants were still in the boot 
till they were in full flower produced no infection. 
LONGEVITY AND VITALITY OF THE ORGANISM 
LONGEVITY 
Within the protective galls, the larvae may retain their vitality for 
many years. According to Needham {18), Baher in 1771 succeeded in 
reviving larvae from galls that had been in the laboratory 27 years. 
